Sulfonimide catalysts for coatings

ABSTRACT

Sulfonimide cure catalysts are used with aminoplast crosslinking agents and resins capable of reacting with aminoplast crosslinking agents to prepare heat curable compositions capable of crosslinking to form coatings and articles. Liquid or solid curable compositions may be prepared. Solid sulfonimide catalysts used in combination with solid glycoluril type crosslinking agents are well suited for powder coating systems containing hydroxy- and carboxy-functional resins.

This is a divisional of application Ser. No. 07/688,022, filed Apr. 19, 1991, now abandoned, which in turn is a C.I.P. of Ser. No. 07/512,041, filed Apr. 26, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to the use of sulfonimide cure catalysts in combination with aminoplast crosslinkers and their use in curable compositions.

BACKGROUND OF THE INVENTION

Alkyl and aryl sulfonic acids have found utility in industry as "strong acid" catalysts capable of activating acid-sensitive curable compositions to produce cured coatings, moulded articles or adhesives.

U.S. Pat. Nos. 3,927,141 and 4,118,437 disclose powder coating compositions containing alkoxyalkyl groups carrying aminoplasts which are cured with an acid catalyst including sulfonic acids, and U.S. Pat. No. 4,064,191 discloses organic solvent-based compositions thereof.

It is well known in the art that strong acids such as sulfonic generally favor rapid cure. However, it is suggested in U.S. Pat. No. 4,031,036, that acid strength alone does not always determine effectiveness of a catalyst in complex reactions. In many cases, strong acids produce less than "smooth" surfaces having a "sandpaper-like" appearance. Furthermore, because of the extreme reactivity of sulfonic acid catalysts, curable powders containing them have been unsatisfactory because of poor package stability. The poor package stability is associated with room temperature crosslinking of the curable powders catalyzed by the excessively strong sulfonic acid catalysts. As a result, the low temperature reaction often causes clumping and sintering or fusing of the powdered resin. These are undesirable because they impair fluidization of the powder during application contributing to the production of non-uniform coatings with diminished gloss.

As a partial solution for low temperature crosslinking, U.S. Pat. Nos. 4,510,290 and 4,281,075 disclose the use of latent-reactive sulfonic acid catalysts such as benzoin tosylates and beta-hydroxy tosylates, respectively. The chemistry of the beta-hydroxy tosylate latent acid catalysts is described in Ind. Eng. Chem. Prod. Res. Dev., 22, 440 (1983). Even though latent catalyst approach improves the shelf-life of the cure catalyst-containing powder coating compositions, the overall film properties and appearance of the cured films have been no better than non-latent sulfonic acid catalyzed systems because the active catalyst in both systems is the same: a sulfonic acid.

Powder coating technology is dominated by isocyanate crosslinked and epoxide crosslinked reaction systems which are of relatively high cost. Improved crosslinking systems based on aminoplast resins when used in combination with solid components offer cost attractive alternative powder coating formulations.

This invention provides sulfonimides as improved catalysts useful in the curing of aminoplast crosslinkable resin compositions with particular utility in powder coatings/formulations.

SUMMARY OF THE INVENTION

This invention is a curable composition comprising:

(i) a sulfonimide cure catalyst,

(ii) an aminoplast crosslinking agent containing at least 2 crosslinkable groups, and

(iii) a polyfunctional material capable of reacting with aminoplast crosslinking agents.

This invention is also a crosslinker/catalyst combination suitable for admixture with an aminoplast crosslinkable resin. The crosslinker/catalyst combination comprises:

(a) a sulfonimide cure catalyst, and

(b) an aminoplast crosslinking agent.

This invention is also a catalyst/polyfunctional material combination suitable for admixture with aminoplast resins, said combination comprising:

(a) a sulfonimide cure catalyst, and

(b) a polyfunctional material capable of reacting with aminoplast crosslinking agents.

This invention is also an improved method of coating substrates by applying to said substrates the curable coating compositions of the invention.

This invention is also a crosslinked article or coating formed from heat-activating the curable compositions of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Curable Coating Compositions

The curable composition of this invention comprises:

(i) a sulfonimide cure catalyst of this invention,

(ii) a crosslinkingly effective amount of an aminoplast crosslinking agent containing at least 2 crosslinkable groups,

(iii) a polyfunctional material capable of reacting with aminoplast crosslinking agents,

(iv) optional ingredients.

SULFONIMIDE CURE CATALYSTS

The novel cure-catalysts of this invention are represented by the Formula:

    RSO.sub.2 NZSO.sub.2 R

wherein each of the R groups is, independently:

(1) a linear, branched, cyclic alkyl, fluoroalkyl, N,N-dialkylamino group of 1 to 20 carbon atoms, or mixtures thereof; or

(2) an aryl group of 1 to 20 carbon atoms containing 5 or less aromatic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴, and R⁵ groups, wherein R¹, R², R³, R⁴, and R⁵ groups are the same or different groups selected from a group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto, vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkyl aminocarbonyl, and N,N-dialkylaminocarbonyl groups; or

(3) an aralkyl group wherein the alkyl and the aryl groups have the same meaning as the alkyl and aryl groups (1) and (2) above; and

wherein the Z group of the formula

(4) hydrogen,

(5) acyl, or

(6) an alkyl or an aralkyl group of 1 to 20 carbon atoms inclusive of sulfonimides as described in DeChristopher, P. J., et. al., J. Amer. Chem. Soc., Vol. 91 (9), p. 2384 (1969) and Curtis, V. A., et. al., Tetrahedron Lett., Vol. 12, p. 199 (1982).

Alkyl or aralkyl groups of (6) which are preferred as the substituent Z are those containing at least one hydrogen at the position beta to the point of attachment of the alkyl group to the nitrogen of the sulfonimide such that upon nucleophilic deacylation reaction of the acylated sulfonimide or upon heat-activated or base-catalyzed elimination or nucleophilic displacement reaction of the alkylated sulfonimide, an unsubstituted sulfonimide is obtained which sulfonimide is represented by the following formula:

    RSO.sub.2 NHSO.sub.2 R

Particularly useful are the sulfonimide cure-catalysts containing both alkyl and aryl groups such as the ortho- meta- and para- isomers of methyl tolyl sulfonimide, or mixtures thereof, the para isomer being preferred, and represented by the formula: ##STR1## wherein the alkyl group imparts solubility and the aryl group contributes to the higher melting point. This combination of substituents produces a solid cure catalyst which is well suited to powder coatings applications.

Diarylsulfonimides are similarly well suited for powder coatings applications because of their higher melting point. Particularly useful in this invention are the para-substituted diarylsulfonimide, having Formula: ##STR2## wherein X is selected from a group consisting of hydrogen, chloro, methyl, nitro, alkyl, amino, cyano, alkoxycarbonyl, carboxyl, acyl, N-alkylaminocarbonyl, and N,N-dialkylaminocarbonyl groups. In the above substituted diarylsulfonimide structure each X may also be substituted in the ortho- or meta- position.

Sulfonimides containing a plurality of imide groups are also usable as catalysts in the compositions of this invention, and can be of two types:

1. Linear polyfunctional sulfonimides, represented by the formula:

    .paren open-st.R--SO.sub.2 NH--SO.sub.2 .paren close-st..sub.n

wherein n groups of the .paren open-st.R--SO₂ NH--SO₂ .paren close-st. units may be the same or different, and the R group in each of the n units is independently selected from the group consisting of:

a. a linear, branched, or cyclic or fluoroalkylene group of 1 to 20 carbon atoms; or

b. an arylene group of 1 to 20 carbon atoms containing 5 or less carbocyclic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴, and R⁵ groups, wherein R¹, R², R³, R⁴, and R⁵ groups are the same or different groups selected from a group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkylaminocarbonyl, and N,N-dialkylaminocarbonyl groups; or

c. an aralkylene group wherein the alkylene and the arylene groups have the same meaning as the alkylene and arylene groups (a) and (b) above; and wherein n is 2 or greater; and

2. Pendant polyfunctional sulfonimides, represented by the Formula:

    P.paren open-st.SO.sub.2 NHSO.sub.2 R).sub.n

wherein P is either a polyfunctional group or a polymer backbone of a molecular weight greater than 500, and R is an alkyl or aryl group of 1 to 20 carbon atoms, and n is 2 or greater.

The amine salts of the sulfonimides of this invention are also usable as latent-reactive cure catalysts in the compositions of this invention. They are represented by the formula: ##STR3## wherein the R groups are, independently: a. a linear, branched, or cyclic alkyl, or fluoroalkyl group of 1 to about 10 carbon atoms, or mixture thereof; or

b. an aryl group of 1 to 20 carbon atoms containing 5 or less carbocyclic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴, and R⁵ groups, wherein R¹, R², R³, R⁴, and R⁵ groups are the same or different groups selected from a group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto, vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkylaminocarbonyl, and N,N-dialkylaminocarbonyl groups, or

c. an aralkyl group wherein the alkyl and the aryl groups have the same meaning as the alkyl and aryl groups in (a) and (b) above.

One, two, or all three R groups of the amine part of the sulfonimide salts can be replaced with one, two or three hydrogen atoms to give secondary ammonium, primary ammonium, or ammonium salts, respectively. Like tertiary amine salts, these are usable in the compositions of the invention as latent-reactive cure catalysts.

The R group in the amine salts above can further be independently interrupted and substituted wtih heteroatoms or heteroatom-containing groups to produce amine salts such as those derived from N,N-dimethylethanolamine, triethanolamine, morpholine, 2-amino-2-methyl-1-propanol, N,N-dimethyl ethanolamine, N-methyl diethanolamine, ethanolamine, diethanolamine, and the like.

The preferred amine salts of the invention are derived from relatively low molecular weight amines which are sufficiently volatile to facilitate the expulsion of the free amines from the cured coatings either before or during the curing process.

Examples of the volatile amines are triethanolamine, diisopropylamine, triisopropylamine, in addition to the heteroatom-containing amines recited above.

The sulfonimide cure catalyst of this invention may take a latent reactive form such as an N-sulfonyl-substituted saccharin which is later reacted with a nucleophile such as ammonia, primary or secondary alcohols, mercaptans, or amines. For example: ##STR4## where, R is an alkyl or aryl group such as shown in the reference: Imai, Y. at. a., Nippon Kagaku Kaishi, No. 1, p. 111 (1982).

The molecular weight of the sulfonimide cure catalyst used in the crosslinker/catalyst ingredient is preferably high enough to make the sulfonimide catalyst a solid at ambient temperatures, and more preferably a solid at above ambient temperatures (viz., about 40° C.) such as those which may be encountered in commercial in-plant storage or transportation environments.

The sulfonimide catalysts are generally prepared by the reaction of sulfonyl chlorides with a sulfonamide in the presence of a base. Typical preparatory methods are taught in U.S. Pat. Nos. 3,052,656 and 4,510,324, Federal Republic of Germany Patent Nos. 765,789, 1,265,157 and 1,235,300, and DDR Patent No. 9132.

CROSSLINKING AGENTS

Crosslinking agents of this invention are aminoplast crosslinkers commonly used in coatings, mouldings, and adhesives. The term "aminoplast" is defined herein as a class of resins prepared by the reaction of an amino group-containing compound and an aldehyde.

The reaction product of amino group-containing compounds and aldehydes is often reacted further with an alcohol to produce partially or fully alkylated derivatives. These derivatives are included in the "aminoplast" definition given above.

The term "aminoplast" as used in the context of this invention also includes phenoplasts (phenolic resins), specifically, the resole-type resins which are the reaction product of phenol and an aldehyde and have the further property of containing pendant hydroxymethyl or alkoxymethyl groups. Resole resins and resolated Novolak resins are examples of phenoplasts suitable as crosslinking agents (see, Kirk-Othmer, "Encyclopedia of Chemical Technology", Vol. 17, 3'd Edition, pages 384-390 (1985) and "Encyclopedia of Polymer Science and Engineering", Vol. 11, 2'd Edition, edited by Mark, Bikales, Overberger, and Menges, (1985) pages 45-57. Commercially avaiable phenoplasts are Bakelite® Phenolic Baking Resins sold by Union Carbide Company, Danbury, Conn., (U.S.A.).

In the preparation of aminoplasts from amino group-containing compounds and aldehydes and subsequent alkylation, dimeric and oligomeric products resulting from self-condensation reaction are often obtained. These oligomeric self-condensation products are also included in the "aminoplast" definition given above.

The aminoplast crosslinking agents of this invention are represented by the formula:

    A--(R).sub.n

wherein the A group in A--(R)_(n) is an n-functional polyamino anchor molecule connected to n(R) groups via the nitrogens and includes the following systems represented by the formulae: ##STR5## wherein R¹ and R² are independently, hydrogen, alkyl or aryl groups of 1 to 10 carbon atoms; ##STR6## wherein R³ is an aliphatic or cycloaliphatic alkyl group, of 1 to 10 carbon atoms, such as methyl, ethyl, butyl, cyclohexyl and the like; or

R³ is an aromatic group, of 1 to 10 carbon atoms, such as phenyl, tolyl, naphthyl, and the like; or

R³ is an aralkyl group, of 1 to 10 carbon atoms, such as benzyl, cumyl, and the like; ##STR7## wherein R is an alkylene or an arylene of 1 to 10 carbon atoms; ##STR8## (i) homopolymers containing acrylamide units of the formula: ##STR9## wherein R is hydrogen or alkyl and m is greater than 2, and copolymers thereof;

(j) polycarbamates;

(k) polyhydantoins;

(l) polyamides;

(m) dialkoxyethylene ureas;

(n) dihydroxyethylene urea represented by the formula: ##STR10## (o) homopolymers containing carbamate units of the formula: ##STR11## wherein R is hydrogen or alkyl, and m is greater than 2, and copolymers thereof;

(p) mixtures of any of (a) through (o); and

wherein the R group in A--(R)_(n) is hydrogen, or an alkyl group of 1 to about 10 carbon atoms, or a crosslinkable group such as --CH₂ OH and --CH₂ OR⁴ wherein R⁴ is an alkyl group of 1 to about 10 carbon atoms or an aminoplast group-containing oligomeric group provided that the total number of the crosslinkable groups per each aminoplast crosslinking agent is at least 2, and preferably more than 2; and

wherein n in A--(R)_(n) is the total functionality of the polyamino anchor molecule A, and is 2 or greater.

The preferred crosslinking agents of this invention are substantially fully etherified, substantially fully methylolated, substantially monomeric aminoplast crosslinkers commonly used in coatings industry. They are characterized by having at least 2, preferably more than 2 crosslinkable groups per crosslinker molecule. It is well known in the art that the minimum number of crosslinkable functional groups required to effect crosslinking is 2 provided that the aminoplast-reactive polyfunctional material has more than 2 functional groups per each molecule. If, on the other hand, the aminoplast-reactive polyfunctional material has only 2 functional groups per each molecule, then each aminoplast crosslinking agent is required to have more than two crosslinkable groups per crosslinker molecule to be capable of producing a crosslinked network.

The most preferred aminoplast crosslinking agents of the invention are selected from a group consisting of substantially fully etherified, substantially fully methylolated, substantially monomeric glycoluril, melamine, benzoguanamine, cyclohexanecarboguanamine, urea, substituted linear and cyclic ureas, and mixtures thereof.

In addition to the substantially fully etherified, substantially monomeric amine-aldehyde aminoplast crosslinking agents described above, the non-etherified or partially etherified substantially fully methylolated or partially methylolated monomeric and oligomeric aminoplasts are also usable in the compositions of this invention. The unetherified or partially etherified aminoplasts generally cure faster than the fully methylolated and etherified aminoplasts in the presence of weaker acid catalyst and may be used advantageously in such cases.

Glycoluril Crosslinkers

The most preferred glycoluril crosslinkers of this invention are N-substituted glycolurils represented by the formula: ##STR12## wherein at least two of the R groups are selected from a group consisting of methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, pentoxymethyl, hexoxymethyl, heptoxymethyl, octoxymethyl, nonoxymethyl, decoxymethyl and mixtures thereof, and the remaining R groups are selected from hydrogen, alkyl, hydroxymethyl, and glycoluril group-containing oligomeric moieties.

While it is preferable to have 4 alkoxymethyl groups per each glycoluril crosslinking agent, under ordinary circumstances it may not be necessary to obtain the pure tetrasubstituted monomeric crosslinker N,N',N",N"'-tetraalkoxymethylglycoluril represented by formula: ##STR13## wherein R is an alkyl group of 1 to about 10 carbon atoms.

The monomeric tetraalkoxyglycolurils themselves are not considered to be resinous materials since they are, as individual entities, non-polymeric compounds. They are considered, however, to be potential resin-forming compounds when subjected to heat, and particularly when subjected to heat under acidic conditions. As a result of the described resin-forming ability, the substantially monomeric glycoluril crcsslinkiers of this invention may contain some higher oligomeric components such as dimers, trimers, and tetramers. The presence of modest amounts of these oligomeric forms is permissible and indeed beneficial in cases where a high melting solid crosslinker is desirable as it is the case in powder coatings.

An example of glycoluril crosslinker of this invention is POWDERLINK® 1174 Powder Crosslinking Agent, a product of American Cyanamid Company, Wayne, N.J., and has the following properties: ##STR14## Non Volatiles, minimum (% by weight): 98 Appearance: White to pale yellow granulated flakes

Melting Point: (°C.) 90°-110° C.

Average Molecular Weight: 350

Equivalent Weight: 90-125

Another example of a glycoluril crosslinker of this invention is CYMEL® 1170 fully butylated glycoluril crosslinker, a product of American Cyanamid Company, Wayne, N.J., having the following properties:

Non Volatiles, minimum (% by weight): 95

Appearance: Clear liquid

Color, Maximum (Gardner 1963): 3

Viscosity (Gardner-Holt, 25° C.): X-Z₂

Molecular Weight, Average: 550

Equivalent Weight: 150-230

Methylol Content: Very low

Urea Crosslinkers

An example of a urea crosslinker usable in this invention is BEETLE® 80 butylated urea-formaldehyde resin, a product of American Cyanamid company, Wayne, N.J., having the following properties:

Appearance: Clear Liquid

Color, Maximum (Gardner 1963): 1

Non-Volatiles (Weight %)*: 96±2

Viscosity (Gardner-Holt, 25° C.): X-Z₃

Solvent Tolerance (ASTM D1198-55): >500

* Foil Method (45° C./45 min.).

Melamine Crosslinkers

The melamine-based aminoplast crosslinking agents are well known in the art and have been used extensively as effective crosslinkers in coatings.

Unlike the tetrafunctional glycolurils, alkoxymethylmelamine functionality can be a maximum of six in a crosslinkingly effective range of 2 to 6 alkoxymethyl groups per each melamine molecule.

Like the glycolurils, alkoxymethyl melamines can contain dimers, trimers, tetramers, and higher oligomers, each given combination of monomers and oligomers being preferred for a given application. For example, the lower viscosity monomer-rich compositions are preferred for solvent-based high solids coatings.

An example of the substantially fully etherified, substantially fully methylolated, substantially monomeric melamines usable in this invention is CYMEL® 303 melamine crosslinking agent, a product of American Cyanamid Company, Wayne, N.J., and has the following properties: ##STR15## Non-Volatiles (% by weight)*: 98 Color, Maximum (Gardner 1963): 1

Viscosity (Gardner-Holt, at 25° C.): X-Z₂

Free Formaldehyde, maximum (weight %): 0.5

Degree of Polymerization: 1.75

* Foil Method (45° C./45 min).

Another example of the substantially fully etherified, substantially fully methylolated, substantially monomeric melamines is CYMEL® 1168 melamine crosslinking agent, a product of American Cyanamid Company, Wayne, N.J. The alkyl group in CYMEL® 1168 consists essentially of a mixture of methyl and isobutyl groups. It has the following properties: ##STR16## Non-Volatiles (% by weight)*: 98 Color, maximum (Gardner 1963): 1

Free Formaldehyde, maximum (weight %): 0.5

Viscosity (Gardner-Holt, at 25° C.): X-Z₂

Equivalent weight: 150-230

* Foil Method (45° C./45 min).

An example of a substantially methylolated, partially etherified, substantially oligomeric melamine is CYMEL® 370 crosslinking agent, a product of American Cyanamid Company, Wayne, N.J. It has the following properties:

Non-Volatiles (% by weight)*: 88±2

Solvent: Isobutanol

Viscosity (Gardner-Holt, at 25° C.): Z₂ -Z₄

Color, maximum (Gardner 1963): 1

Equivalent Weight: 225-325

* Foil Method (45° C./45 min)

Guanamine Crosslinkers

As in melamines, the partially or fully methylolated or etherified alkyl and aryl guanamine aminoplasts, both in their monomeric and oligomeric forms, are usable as crosslinking agents in this invention, with the selection depending on the particular application or the properties desired in the product.

Benzoguanamine, cyclohexylcarboguanamine and acetoguanamine aminoplasts are especially preferred as crosslinkers in this invention. The benzoguanamine crosslinkers are represented by the formula: ##STR17## wherein R is an alkyl group of 1 to about 10 carbon atoms, or a mixture thereof. An example of a benzoguanamine-based crosslinking agent is CYMEL® 1123 Resin as described above, and wherein R is a mixture of methyl and ethyl groups.

The acetoguanamine-based crosslinkers are represented by the formula: ##STR18## wherein each R is independently an alkyl group of 1 to about 10 carbon atoms.

The cyclohexylcarboguanamine-based crosslinkers are represented by the formula: ##STR19## wherein each of the R groups is independently an alkyl group of 1 to about 10 carbon atoms, or a mixture thereof.

It is evident from the discussions above, that a person skilled in the art, in selecting the most suitable crosslinker for a particular application, may choose a mixture thereof which imparts a balance of properties desired for that particular application.

RATIO AND PROPORTIONS OF INGREDIENTS

The aminoplast crosslinking agent (ii) is combined with the polyfunctional aminoplast-reactive ingredient (iii) in proportions that give weight ratio of the ingredients (ii):(iii) ranging from about 1:40 to about 3:1.

The weight ratio of the sulfonimide catalyst (i) to the aminoplast crosslinking agent (ii) is from about 1:4 to about 1:400.

The effective concentration of the sulfonimide cure catalyst is from about 0.01 to about 10 weight percent based on the total weight of resin solids. It is preferably from 0.3 to 0.8 weight percent of the total resin solids.

OPTIONAL INGREDIENTS

The optional ingredients present in the curable composition of the invention vary depending on the intended use of the cured article or film.

Suitable optional ingredients include fillers, ultraviolet light stabilizers, pigments, flow control agent, plasticizers, mold release agents, and corrosion inhibitors.

The composition of the invention may contain as an optional ingredient a liquid medium. Such a medium may be used to aid the uniform application and transport of the curable composition. Any or all of the ingredients of the composition may be contacted with the liquid medium. Moreover, the liquid medium may permit formation of a dispersion, emulsion, invert emulsion, or solution of the curable composition ingredients. Particularly preferred is a liquid medium which is a solvent for the curable composition ingredients (i), (ii), and (iii). Suitable solvents are selected from alcohols, ketones, ethers, esters, water, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons and mixtures thereof.

POWDER COATING COMPOSITION

The novel curable powder coating composition of this invention comprises:

(i) a sulfonimide cure catalyst of this invention,

(iii) a polyfunctional material capable of reacting with aminoplast crosslinking agents,

(iii) a crosslinkingly effective amount of a aminoplast crosslinking agent containing at least 2 crosslinkable groups,

(iv) optional ingredients.

It is necessary that at least one of the powder coating ingredients (i), (ii), (iii) or (iv) be a solid, with the proviso that the solid ingredient(s) of the powder coating comopsition be capable of retaining the non-solid ingredient(s) to give a composition that as a whole is a solid.

A much preferred embodiment of the invention is a composition wherein the powder coating ingredients (i), (ii), (iii), and (iv) are all solids having the form of a flowable powder.

In recent years, powder coating technology has been the subject of considerable interest and commercial growth. Because powder coatings are all solids systems, they do not suffer from the solvent-related disadvantages of the solvent-based coatings systems. Powder coating minimizes the cost of shipping, storing, handling, and solvent waste disposal.

In powder coatings the ingredients used are essentially similar to conventional liquid coatings except that the powder coating composition is required to be a solid.

Preferred Powder Coating Compositions:

Preferred powder coating compositions are those wherein the ingredients (i), (ii), (iii) and (iv) are all solids. More particularly, the individual composition ingredients are as described below:

(i) The novel sulfonimide cure catalysts usable in powder coatings are the sulfonimides of this invention having melting points ranging from about 40° C. to about 250° C., and more preferably ranging from about 80° C. to about 180° C.

(ii) The polyfunctional materials usable in powder coatings are the polyfunctional materials of this invention having a glass transitions (Tg) ranging from about 40° C. to about 150° C., and softening points ranging from about 40° C. to about 150° C., and more preferably ranging from about 80° C. to about 140° C.

It is preferable that the powder coating composition as a whole be a solid at ambient temperatures and that it remains solid up to about 40° C. to preserve the powdery state of the curable composition and to prevent lumping.

Upon heating, however, these resins should become fluid to permit formation of low viscosity melts which allow efficient mixing of the components of the curable composition prior to crosslinking. It is desirable that the aminoplast-reactive resins become fluid at temperatures ranging from about 80° C. to about 150° C., and most preferably from about 100° C. to about 140° C.

(iii) The aminoplast crosslinking agents usable in powder coatings are the solid aminoplast crosslinking agents of this invention having melting or softening points ranging from about 40° C. to about 150° C., and more preferably from about 80° C. to about 140° C., and most preferably from about 100° C. to about 120° C.

Glycoluril type aminoplast crosslinking agents are particularly preferred because they are solids at ambient temperatures and generally have suitable melting points.

It is preferable that the solid aminoplast crosslinking agents are solids at ambient temperatures and that they remain solids up to about 40° C. to preserve the powdery state of the curable composition and to prevent lumping. It is desirable that the aminoplast crosslinking agents become fluid at temperatures ranging from about 80° C. to about 150° C., and more preferably from 100° C. to about 140° C.

(iv) The curable powder coating compositions may include varying amounts of optional ingredients such as benzoin at about 1 to 4 weight percent level. The composition may also include as a flow control agent ingredients such as Modaflow® Powder III Resin Modifier, a product of Monsanto Company, or Resiflow P-67 Flow Control Agent, a product or Estron Chemical, Inc. at about 1 to 2 weight percent level. Moreover, fillers and pigments such as titanium dioxide based pigments may be conventionally added to improve the appearance and properties of the coatings and articles formed from the compositions.

POLYFUNCTIONAL MATERIALS

The polyfunctional material capable of reacting with an aminoplast crosslinking agent is one of three essential components required for the curable compositions of this invention. The other essential components are aminoplast crosslinking agents such as N,N',N",N"'-tetramethoxymethylglycoluril, and sulfonimide cure catalyst such as N-(methanesulfonyl)-p-toluenesulfonamide. The aminoplast-reactive functional groups of the polyfunctional material react, under cure conditions, with crosslinkable groups to produce a three dimensional crosslinked network such as those found in coatings, moulded articles and adhesives.

The aminoplast reactive functional groups are selected from a group comprising: amino groups, amido groups, carboxyl groups, mercapto groups, hydroxy groups, and combinations of any of the aforementioned functional groups. Reactive materials having a plurality of carboxy and/or hydroxy groups are particularly preferred in the practice of the invention.

Suitable polyfunctional hydroxy reactant materials may be epoxy or polyurethane prepolymers, alkyds, acrylic resins containing pendant or terminal carboxy or hydroxy functionalities, or polyester resins with pendant or terminal hydroxy or carboxy groups. These are described in greater detail below.

In cases where resins used in the formulations of this invention are intended for powder coating applications, the resins should be solids at ambient temperatures and should remain solids up to about 40° C. to preserve the powdery state of the curable composition and prevent lumping. The aminoplast-reactive materials or resins used in the compositions of the invention preferably have a molecular weight of from about 100 to about 50,000. In the event that the aminoplast reactive material is in the form of an emulsion the molecular weight may be as high as about 5,000,000.

1. Acrylic Resin Aminoplast-Reactive Material

The hydroxyfunctional acrylio resins used in formulating the curable compositions of this invention preferably have molecular weights in the range of from about 500 to about 50,000 and hydroxyl group equivalent weights of from about 200 to 4,000. An examples of a suitable acrylic resin is JONCRYL® SCX-800 A acrylic resin, a product of S.C. Johnson and Sons, Inc., having the following physical and chemical properties:

Non-Volatiles (weight %): 98

Hydroxyl Number: 43

Equivalent Weight: 1300

Softening Point (°C.): 100

Glass Transition Temperature (Tg) (°C.): 43

Acid Value (mg KOH/g): 15

ICI Viscosity (200° C., Poise): 25

Another example of a suitable acrylic resin is JONCRYL® BCX-800 B acrylic resin, a product of S.C. Johnson and Sons, Inc., having the following physical and chemical properties:

Non-Volatiles (weight %): >97

Hydroxyl Number: 40

Glass Transition: Temperature (Tg) (°C.): 43

Acid Value: 15-20

Softening Point (°C.): 107

Equivalent Weight: 1402

ICI Viscosity: (200° C., Poise): 45-50

or JONCRYL® 500 acrylic resin, a product of S.C. Johnson and Sons, Inc., having the following properties:

Viscosity (centipoise): 4000

Solids Content (%): 80

Hyroxyl Number (based on solids): 140

Equivalent Weight (based on solids): 400

Molecular Weight (Mn)*: 1300

Polydispersity (Mw/Mn)**: 1.7

* Mn=Number Average Molecular Weight.

** Mw=Weight Average Molecular Weight.

Commercially available acrylic resins are generally applicable for use in preparing the compositions of the invention. Selection of the optimum acrylic resin will depend on the user's desire to impart to the final cured product particular physical properties such as hardness, flexure, chemical and solvent resistance, and etc.

2. Polyester Resins

The hydroxy functional polyester resins used in formulating the curable compositions of this invention preferably have molecular weights in the range of from about 1,000 to 50,000 and hydroxyl group equivalent weights of from about 200 to 4,000.

An example of a suitable polyester resin is Arakote® 3109 solid hydroxyl terminated polyester powder coating resin, a product of Ciba-Geigy Corporation, Hawthorne, N.Y., having the following physical and chemical properties:

    ______________________________________                                         Color               Colorless Solid                                            OH Number:          27-32                                                      ICI Viscosity at 200° C. (Poise):                                                            40                                                        Glass Transition Temperature                                                                        66                                                        (Tg) (°C.):                                                             Equivalent Weight:  1900                                                       ______________________________________                                    

Another example of a suitable polyester resin is ALFTALAT® AN 745 hydroxyfunctional polyester resin, a product of Hoechst Corporation, having the following physical and chemical properties:

Color, 50% (ASTM D 1544-68): 3

OH Number: 30

Equivalent Weight: 1870

Acid Value (mg KOH/g): 8

Glass Transition Temperature (Tg) (°C.): 55

ICI Viscosity (200° C., Poise): 50-65

Another example of a suitable polyester resin is ARAKOTE® 3010 carboxyl-terminated polyester, a product of Ciba-Geigy Corporation, Ardsley, N.Y., having the following properties:

Color, Maximum (Gardner, ASTM D 2849): 2

OH Number: ≦7

Acid Value (mg KOH/g): 27-33

ICI Viscosity (200° C., Poise): 35-60

Glass Transition Temperature (Tg) (°C.): 62

Equivalent Weight: 1800

Another example of a suitable polyester resin is RUCOTE® 101 polyester resin, a product of Ruco Polymer Corporation, Hicksville, N.Y., having the following physical and chemical properties:

Appearance: granular solid

Softening Temperature (°C.): 120

OH Number: 29

Acid Value (mg KOH/g): 1

Glass Transition Temperature (Tg) (°C.): 53

Equivalent Weight: 2000

ICI Viscosity (200° C., Poise): 53

Another example of a suitable polyester resin is CARGILL 3000 polyester, a product of Cargill Corporation, having the following physical and chemical properties:

OH Number: 50

Equivalent Weight: 1035

Glass Transition (Tg) (°C.): 56

Acid Value (mg KOH/g): 15

Upon cure, polyester resins give films of superior properties, as described in detail in the Examples. A wide variety of commercial polyester resins may be used for the aminoplast-reactive ingredient of the invention, provided such resins have the physical properties suitable for the intended application.

3. Other Aminoplast-Reactive Systems

Other polyhydroxy functional compounds which are useful in the practice of the invention are diols, triols, tetraols, and higher polyhydroxy alcohols. Illustrative polyhydric alcohols are pentaerythritol dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, anhydroenneahepititol, 1,2,4-butanetriol, and 1,2,6-hexanetriol. These polyols can also be used to totally or partially replace the acrylic resin or polyester resin aminoplast-reactive ingredient of the composition of the invention. However, the film properties resulting from addition of such non-resinous ingredients sometimes are inferior and lack flexibility in the cured film final product.

Polyfunctional epoxy prepolymers, alkyds, and polyurethane prepolymers are also usable as hydroxyfunctional aminoplast-reactive materials.

Polyfunctional amides are also suitable as aminoplast-reactive components, provided they have the proper physical properties suitable for the intended use. For example, for powder coatings application, they are solids at up to about 40° C. to allow the preparation of storage stable powders containing the aminoplast crosslinking agents. The crosslinked films and articles resulting from polyamide-containing curable compositions, however, have physical properties somewhat different (i.e. harder) than polyester and acrylic-based systems described above.

THE CATALYST/CROSSLINKER COMBINATION

The catalyst/crosslinker combination of the invention is a uniform mixture of the following materials:

(a) a sulfonimide cure catalyst, and

(b) an aminoplast crosslinking agent containing at least two crosslinker groups.

Suitable sulfonimide cure catalysts (a) and aminoplast crosslinking agents (b) are as set out in the preceding sections. The components (a) and (b) can each be either liquids or solids. A particularly preferred catalyst/crosslinker combination is one wherein both the sulfonimide catalyst (a) and the aminoplast crosslinker (b) are both solids at 40° C.

THE IMPROVED METHOD OF COATING BY THIS INVENTION

This invention is also an improved method of coating substrates by applying to substrates the coating composition of the invention.

a Method of Coating Using Liquid Coating Compositions:

This invention is a method of coating substrates using a liquid curable coating composition, where the composition contains the following ingredients:

(i) a sulfonimide cure catalyst,

(ii) a crosslinkingly effective amount of an aminoplast crosslinking agent containing at least 2 crosslinkable groups,

(iii) a polyfunctional material capable of reacting with aminoplast crosslinking agents, and

(iv) a liquid medium.

The liquid curable coating composition of the invention may be contacted with a substrate by spraying, padding, brushing, rollercoating, curtaincoating, flowco,ting, electrostatic spraying, electrocoating or dipping.

A Method of Coating Using Powder Coating Compositions:

"Powder coating" is an art recognized process and is defined herein as a method of electrostatic powder-spraying wherein a finely divided solid coating material is electrostatically attracted to a surface of an article. Alternatively, the powder coating composition may be contacted with the substrate by immersing the substrate in fluidized bed of powder. The article covered with the powder is heated to at least the fusion temperature of the coating composition forcing it to flow out and form a coating which is cured by further application of heat.

The prior art powder coating process can be considerably improved by using as the coating material a low temperature heat-curable aminoplast coating composition comprising as essential ingredients:

(i) a solid sulfonimide cure catalyst of this invention,

(ii) a solid polyfunctional aminoplast-reactive material, and

(iii) a solid aminoplast crosslinking agent.

The unexpectedly superior properties of the films formed from the powder coating compositions of the invention are their superior appearance manifested in gloss and smoothness, improved impact and corrosion resistance.

A typical procedure for using the compositions of the invention is as follows:

The substrates are coated with the powder coating composition of the invention and subjected to a temperature of from about 90° C. to about 350° C. to melt and spread the composition uniformly onto the substrate surface. Thereafter, the substrate is held at a temperature of from about 120° C. to about 350° C. to crosslink the composition and form the permanently cured coating.

CATALYST/POLYFUNCTIONAL MATERIAL COMBINATION

The catalyst/polyfunctional material combination of the invention is a uniform mixture of the following materials:

(a) a sulfonimide cure catalyst, and

(b) a polyfunctional material capable of reacting with aminoplast crosslinking agents.

Suitable sulfonimide cure catalysts (a) and suitable polyfunctional materials capable of reacting with aminoplast crosslinking agents (b) are set out in the preceeding sections.

The components (a) and (b) can each be either liquids or solids. A particularly preferred catalyst/polyfunctional material combination is one wherein the sulfonimide cure catalyst (a) and the polyfunctional material capable of reacting with aminoplast crosslinking agents (b) are both solids at 40° C. In the preferred mode, components (a) and (b) are blended to form a masterbatch, which is then admixed with an aminoplast crosslinking agent. Optionally, the masterbatch is admixed with an aminoplast crosslinking agent and an additional amount of polyfunctional material.

The suitable weight ratio of the catalyst (a) to polyfunctional material (b) is in the range of from about 1:10,000 to about 9:1, with ratios of from about 3:1 to about 1:20 being preferred.

The solid sulfonimide cure catalyst/polyfunctional material combinations of the invention are prepared by a process comprising the steps of:

(a) heating a mixture of a solid sulfonimide cure catalyst and a solid polyfunctional material at a temperature sufficient to produce a uniform melt-mixed resinous material,

(b) cooling said melt-mixed resinous material to a temperature sufficient to produce a solid, and

(c) crushing the solid to produce a powdered sulfonimide cure catalyst/polyfunctional material combination usable in the improved method of powder coating described hereinbelow.

IMPROVED METHOD OF POWDER COATING WITH CATALYST/POLYFUNCTIONAL MATERIAL COMBINATION

An improved method of coating substrates by contacting said substrates with a powder coating composition and thereafter heat curing said composition, wherein the improvement comprises: contacting said substrate with a curable powder coating composition comprising:

(i) a combination of sulfonimide cure catalyst/polyfunctional material capable of reacting with aminoplast crosslinking agents,

(ii) a crosslinkingly effective amount of an aminoplast crosslinking agent containing at least 2 crosslinkable groups,

(iii) optionally, an additional amount of a polyfunctional material capable of reacting with aminoplast crosslinking agents, and

(iv) other optional ingredients known to be usable in powder coatings technology.

The improved method of powder coating employs a preblended mixture of the sulfonimide cure catalyst and the polyfunctional material which mixture is further blended with the remaining ingredients and the resulting powder is applied to substrates to be coated by methods well known in the art as "Powder Coating," defined and briefly described in a preceeding section entitled "A Method of Coating Using Powder Coating Compositions."

Suitable sulfonimide cure catalysts, and polyfunctional materials capable of reacting with aminoplast crosslinking agents are set out in the preceeding sections. The ratios of the ingredients are futher described below.

The sulfonimide cure catalyst/polyfunctional material combinations (i) are those previously described under the same title. In the masterbatch of catalyst/polyfunctional material combination (i), the suitable weight ratio of the sulfonimide cure catalyst to polyfunctional material is in the range of from about 1:10,000 to about 9:1, with a ratio of about 1:1 being preferred. The weight percent of the sulfonimide cure catalyst in the catalyst/polyfunctional material combination of ingredient (i) is from about 0.01 percent to about 90 percent, with 50 weight percent being preferred.

In the curable compositions of the improved method of powder coating, the weight percent of the sulfonimide cure catalyst/polyfunctional material ingredient (i) is in the range of 0.01 to 97.5 percent of the total weight of the resin-forming ingredients, with 1.0 percent being preferred. The weight ratio of the aminoplast crosslinking agent to total polyfunctional material is from about 1:40 to about 3:1, and the weight precent of the sulfonimide cure catalyst is in the range of 0.01 to about 10 weight percent of the total weight of the resin-forming ingredients.

"Resins-forming ingredients" are defined herein as the sum of the total polyfunctional material and the aminoplast crosslinking agent. Other ingredients are excluded from the above definition.

CROSSLINKED ARTICLES AND COATINGS FORMED BY THE COMPOSITIONS OF THIS INVENTION

The curable compositions of this invention containing the sulfonimide cure-catalyst of the invention can be heat cured (typically 90° C. to 400° C.) to produce crosslinked moulded articles, adhesives and coatings. Because of the polyfunctional nature of the reactants, the resulting product in this case is a crosslinked article in the form of a film such as adhesives and/or coatings or the form of an article such as molded products.

The heat-cured compositions of this invention may be employed as coatings for wire, appliances, automotive parts, furniture, pipes, machinery, and the like.

The heat-cured compositions may also be used to form solid articles such as cases, enclosures, and structural members.

The following Examples illustrate various embodiments of the invention.

EXAMPLE 1 Preparation of the Sulfonimide Cure Catalysts*

Part A

p-Toluenesulfonyl chloride (38.2 g, 0.20 mole) was added, in five portions over a period of 90 minutes, to a heated (70° C.) solution of methanesulfonamide (19.0 g, 0.20 mole) in aqueous sodium hydroxide (176 ml). Throughout the addition, a pH of 12 was maintained by frequent additions of aqueous 5% sodium hydroxide solution. After stirring for about 20 hours at about 70° C., the reaction mixture was cooled to room temperature and acidified with concentrated hydrochloric acid to pH less than 1 and extracted with dichloromethane (3×200 ml). The organic layer was separated, dried (sodium sulfate) and concentrated to 150 ml. Addition of n-heptane (200 ml) gave highly pure methyl para-tolyl sulfonimide, also known as N-(methanesulfonyl)-p-toluenesulfonamide, a sulfonimide cure catalyst of the invention, as a white precipitate (18.3 g), m.p. 117°-120° C.

Example 1, Part A illustrates the preparation of a mixed aryl and alkyl group containing cure catalyst of this invention.

* Prepared by the general procedure described in the following reference article: N. N. Dykhanov, Zhur. Obshchei Khim., 29, 3602 (1959); Chemical Abstracts (54) 19577g (1960).

Part B

The procedure of EXAMPLE 1, PART A was followed with the exception that methanesulfonamide was replaced with an equivalent amount of p-toluenesulfonamide (34.2 g, 0.20 mole) and the extraction step was replaced by a purification step to give the symmetrical di-(p-toluene)sulfonimide, a sulfonimide cure catalyst of the invention, as a white solid of 96% purity, m.p. 171°-173° C.

EXAMPLE 1, PART B illustrates the preparation of the symmetrical di-(p-toluene)sulfonimide, which is another example of the sulfonimide cure catalysts of this invention.

Part C

A commercially available sulfonimide, N-(4-aminobenzenesulfonyl)benzenesulfonamide, a product of Aldrich Chemicals, Milwaukee, Wisc., was used as cure catalyst in the preparation of Composition C.

Part D

The procedure of EXAMPLE 1, PART A, was followed with the exception that methanesulfonamide and p-toluenesulfonyl chloride were replaced, respectively, with equivalent amounts of p-nitrobenzenesulfonamide and a solution of p-nitrobenzenesulfonyl chloride in acetone (50 ml). also, the extraction step was replaced with a purification step to give the symmetrical di-(4-nitrobenzene)sulfonimide, a sulfonimide cure catalyst of the invention, as an off-white solid of 98% purity, m.p. 238°-240° C.

EXAMPLE 1, PART D illustrates the preparation of another example of sulfonimide cure catalyst of this invention.

EXAMPLE 2

This example illustrates the preparation of powder coatings using the sulfonimide cure catalysts of the invention.

The following four curable compositions, Composition A, B, C, and D, were formulated using sulfonimide cure catalysts of this invention and thereafter cured at 190° C. (20 min). 1. PREPARATION OF THE CURABLE COMPOSITIONS

    ______________________________________                                                                 Weight (g)                                             ______________________________________                                         A.   COMPOSITION A                                                                  Arakote ® 3109 Polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide Cure Catalyst of Example 1,                                                                 0.50                                                  Part A                                                                         Benzoin (a solid additive)                                                                              1.40                                                  R960-48 ® Titanium Dioxide Pigment                                                                  40.00                                                 (product of DuPont Company,                                                    Wilmington, Delaware)                                                          Resiflow P-67 Flow Control Agent                                                                        1.30                                                  (product of Estron Chemical, Inc.                                              Culvert City, Ky)                                                         B.   COMPOSITION B                                                                  Arakote  ® 3109 Polyester (solid)                                                                   94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide Cure Catalyst of Example 1,                                                                 0.50                                                  Part B                                                                         Benzoin (a solid additive)                                                                              1.40                                                  R960-48 Titanium Dioxide Pigment                                                                        40.00                                                 Resiflow P-67 Plow Control Agent                                                                        1.25                                             C.   COMPOSITION C                                                                  Arakote ® 3109 Polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide Cure Catalyst of Example 1,                                                                 0.50                                                  Part C                                                                         Benzoin (a solid additive)                                                                              1.40                                                  R960-48 Titanium Dioxide Pigment                                                                        40.00                                                 Resiflow P-67 Flow Control Agent                                                                        1.25                                             D.   COMPOSITION D                                                                  Arakote ® 3109 Polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide Cure Catalyst of Example 1,                                                                 0.50                                                  Part D                                                                         Benzoin (a solid additive)                                                                              1.40                                                  Titanium Dioxide Pigment 40.00                                                 Resiflow P-67 Flow Control Agent                                                                        1.25                                             ______________________________________                                    

A control composition was prepared as described above in Composition A with the exception that no cure catalyst was used.

All components were dry-blended in a Waring blender or a Welex mixer for small and larger scale runs, respectively. The dry-blended powder was then melt-mixed at about 90° C. to 135° C. for 1-5 minutes in a two roll mill to allow homogeneous mixing without allowing crosslinking to occur. The melt-mixed material was then chopped into smaller pieces in a blender mill or a pelletizer, and fed into a mill classifier where the chips were ground to a fine powder with particle size about 35 microns. The finely ground powder, charged with up to so KV power, was then sprayed through an electrostatic spray gun on grounded metal substrates, Bonderite® 1000 (a product of Parker Industries, Inc.) in a spray booth.

2. Curing the Curable Composition

The electrostatically coated Bonderite 1000 substrates containing the curable compositions of the invention were then baked in an oven at 190° C. to allow the powder to fuse, flow out and crosslink. These processes were analyzed by means of a viscometer and a rheometer.

TABLE 1 summarizes the cure conditions, the film properties resulting from curing the curable compositions and particularly the film appearance.

It is concluded from the results in EXAMPLE 2 that powder coatings prepared by using the curable compositions of this invention which contain the cure catalysts of this invention have excellent film properties and appearance. The control formulation without catalyst did not cure, showing the necessity of catalyst inclusion in the formulation.

                                      TABLE 1                                      __________________________________________________________________________     POWDER COATINGS FROM CURABLE COMPOSITIONS                                      OF THE INVENTION CURE CONDITIONS,                                              FILM PROPERTIES AND APPEARANCE                                                              CURABLE COMPOSITIONS*                                                          Comp.  Comp.  Comp.  Comp.                                                     A      B      C      D                                            __________________________________________________________________________     CURE CONDITIONS                                                                Catalyst of  Part A Part B Part C Part D                                       Example 1                                                                      Weight of    0.50   0.50   0.50   0.50                                         Catalyst (g)                                                                   Bale Temperature                                                                            190    190    190    190                                          (°C.)                                                                   Bake Time (min.)                                                                            20     20     20     20                                           FILM APPEARANCE                                                                             Orange Orange Orange Orange                                                    Peel   Peel   Peel   Peel                                                      Microblisters                                                                         Microblisters                                                                         Microblisters                                                                         Microblisters                                                    Craters       Pinholes                                                                       Gel Seed                                     FILM PROPERTIES                                                                Film Thickness                                                                              1.9-2.3                                                                               1.9-2.5                                                                               1.4-2.4                                                                               1.0-2.0                                      (mils)                                                                         (ASTM D-1400-81)                                                               Film Thickness                                                                              0.048-0.058                                                                           0.048-0.064                                                                           0.036-0.061                                                                           0.025-0.050                                  (mm)                                                                           (ASTM D-1400-81)                                                               Hardness, KHN.sub.25                                                                        13.0   11.7   10.2   12.2                                         ASTM (D-1474-85)                                                               MEK Rubs     200+   200+   200+   200+                                         (Double Rubs)                                                                  Impact, F/R  160/160                                                                               160/160                                                                               160/160                                                                               160/160                                      in lb)                                                                         (Front/Reverse)                                                                ASTM D-2794-82                                                                 Color, Tristim-                                                                             -0.06  -0.03  0.00   0.02                                         ulus                                                                           Gloss, 60°                                                                           94.1   94.0   94.1   78.4                                         Gloss, 20°                                                                           79.4   73.4   79.3   32.5                                         RESISTANCE                                                                     PROPERTIES                                                                     Humidity (60° C.)                                                                    504    528    504    456                                          Time (hrs)                                                                     ASTM D 4585-87                                                                 Appearance   No     No     No     Dense                                        After Testing                                                                               Change Change Change Micro-                                                                         blisters                                     Salt Spray,  1008   1008   1008   1032                                         Time (hrs)                                                                     ASTM B-117                                                                     Creepage (mm)                                                                               3      0      0      0                                            Appearance** 9      9      9      9                                            after testing                                                                  ASTM D-610                                                                     __________________________________________________________________________      *The control composition containing no catalyst did not cure well under        the conditions of EXAMPLE 2. The film was removed completely in less than      2 MEK double rubs.                                                             **Scale is 1 to 10 where 10 is the best.                                 

EXAMPLE 3

The experiments of EXAMPLE 2 were repeated with Compositions A, B, C, and D at the slightly lower temperature of 175° C. Composition C did not cure well. The cure conditions, film properties and film appearance of the remaining compositions are summarized in TABLE 2.

It is concluded from the results in TABLE 2 that the curable compositions of this invention containing the sulfonimide cure catalysts are capable of curing at low temperatures (175° C.) to produce powder coatings with excellent film properties and acceptable appearance.

                  TABLE 2                                                          ______________________________________                                         Powder Coatings from Curable Compositions                                      of the invention                                                                         CURABLE COMPOSITIONS                                                           Comp.   Comp.        Comp.                                                     A       B            D                                               ______________________________________                                         FILM        Orange    Orange       Orange                                      APPEARANCE  Peel      Peel         Peel                                                    Micro-    Micro-       Micro-                                                  blisters  blisters     blisters                                                          Craters                                                  FILM                                                                           PROPERTIES                                                                     Film Thickness                                                                             1.8-2.8   2.5-3.5      1.5-2.5                                     (mils)                                                                         Film Thickness                                                                             0.046-0.071                                                                              0.064-0.089  0.038-0.064                                 (mm)                                                                           Hardness KHN.sub.25                                                                        11.8      12.7         10.5                                        MEK Rubs       20/200+                                                                                  10/200+   200+                                        Impact F/R (in-lb)                                                                         160/160   100-120/0-20 160/160                                     Color, Tristim-                                                                            -0.06     -0.03        0.05                                        ulus                                                                           Gloss, 60°                                                                          67.4      68.3         58.9                                        Gloss, 20°                                                                          47.3      38.3         24.5                                        RESISTANCE                                                                     PROPERTIES                                                                     Humidity (60°C.),                                                                   456       288          192                                         Time (hrs)                                                                     Appearance  Increased Increased    Increased                                   after testing                                                                              Microblis-                                                                               Micro-       Micro-                                                  ters, some                                                                               blisters     blisters                                                loss of                                                                        gloss                                                              Salt Spray, 1008      1008         1008                                        Time (hrs)                                                                     Creepage (mm)                                                                              2         0            0                                           Appearance  9         9            9                                           (after testing)                                                                ______________________________________                                    

EXAMPLE 4

Comparative

Curable compositions E, F, and G were prepared and cured at 190° C./20 min. by the method described in EXAMPLE 2.

    ______________________________________                                                                Weight (g)                                              ______________________________________                                         COMPOSITION E                                                                  Arakote ® 3109 polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide cure catalyst of EXAMPLE 1,                                                                 0.30                                                  PART A                                                                         Benzoin (a solid additive)                                                                              1.40                                                  R960-48 titanium dioxide pigment                                                                        40.00                                                 Resiflow P-67 flow control agent                                                                        1.30                                                  COMPOSITION F                                                                  Arakote ® 3109 polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  p-Toluenesulfonic Acid Monohydrate (solid)                                                              0.30                                                  Benzoin (a solid additive)                                                                              1.40                                                  OR 650 titanium dioxide pigment                                                                         40.00                                                 Resiflow P-67 flow control agent                                                                        1.25                                                  COMPOSITION G                                                                  Arakote ® 3109 polyester (solid)                                                                    94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)            6.00                                                  p-Toluenesulfonic acid monohydrate (solid)                                                              0.20                                                  Benzoin (a solid additive)                                                                              1.40                                                  R960 48 titanium dioxide pigment                                                                        40.00                                                 Modaflow III flow control agent                                                                         1.25                                                  ______________________________________                                    

TABLE 3 summarizes the film properties and appearance characteristics of the cured coatings obtained by curing the compositions E, F, and G.

It is concluded from the results in EXAMPLE 4 that the curable composition E of this invention containing the sulfonimide cure catalyst of EXAMPLE 1, PART A produces superior powder coatings when compared with curable compositions of the prior art such as compositions F and G containing p-toluenesulfonic acid catalyst commonly used in prior art. The prior art p-toluenesulfonic acid cured system gave unacceptable appearance, lower gloss, and failed in the salt spray test.

                                      TABLE 3                                      __________________________________________________________________________     Comparison of Sulfonimide Cure Catalyst with p-Toluenesulfonic Acid in         Powder Coatings                                                                                CURABLE COMPOSITIONS                                                           Comp.    Comp.  Comp.  Comp.   Comp.                                           E.sup.1  F.sup.2                                                                               G.sup.3                                                                               F.sup.4 G.sup.4                         __________________________________________________________________________     FILM APPEARANCE Orange Peel                                                                             Orange Peel                                                                           Orange Peel                                                                           Orange Peel                                                                            Orange Peel                                     Microblisters                                                                           Microblisters                                                                         Microblisters                                                                         Microblisters                                                                          Microblisters                                            Pinholes                                                                              Matted Craters Pinholes                                                 Gel Seeds     Gel Seed                                                                               Craters                                                                        Gel Seed                        FILM PROPERTIES                                                                Film Thickness  2.4-2.9  1.7-3.0                                                                               1.9-2.2                                                                               1.9-3.3 2.4-3.3                         (mils)                                                                         Film Thickness  0.061-0.074                                                                             0.043-0.076                                                                           0.048-0.056                                                                           0.048-0.084                                                                            0.061-0.084                     (mm)                                                                           Hardness KHN.sub.25                                                                            12.1     12.0   10.8   10.6    10.1                            MEK Rubs           20/200+                                                                              200+   200+   200+    200+                            Impact F/R (in-lb)                                                                             160/160  160/160                                                                               45-50/45-50                                                                            60-80/80-100                                                                          140-160/40-60                   Color, Tristim- -0.06    0.01   -0.05  -0.03   -0.02                           ulus                                                                           Gloss, 60°                                                                              92.7     83.7   70.3   88.3    86.5                            Gloss, 20°                                                                              78.6     42.9   25.0   48.1    48.5                            RESISTANCE PROPERTIES                                                          Humidity (60° C.),                                                                      456      504    120                                            Time (hrs)                                                                     Appearance      Increased                                                                               No change                                                                             Increased                                      (after testing) Microblisters,  Microblisters                                                  slight loss of gloss                                           Salt Spray,     1008     768    192                                            Time (hrs)                                                                     Creepage (mm)   1        3      0                                              Appearance      9                                                              (after testing)                                                                __________________________________________________________________________      .sup.1 0.3% N(Methanesulfonyl)-1-toluenesulfonamide cure catalyst, based       on weight of resin solids.                                                     .sup.2 0.3% pToluenesulfonic acid monohydrate cure catalyst, based on          weight of resin solids.                                                        .sup.3 0.2% pToluenesulfonic acid monohydrate cure catalyst, based on          weight of resin solids.                                                        .sup.4 Repeat experiments.                                               

EXAMPLE 5

Curable composition H was prepared by the method described in EXAMPLE 2. It was cured at 175 and 190° C. by the method described in EXAMPLE 2.

    ______________________________________                                         COMPOSITION H            Weight (g)                                            ______________________________________                                         Alftalat ® AN 745 polyester (solid)                                                                 94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide cure catalyst of EXAMPLE 1,                                                                 0.50                                                  PART A                                                                         Benzoin (a solid additive)                                                                              2.40                                                  R960-48 titanium dioxide pigment                                                                        40.00                                                 Resiflow III flow control agent                                                                         1.30                                                  ______________________________________                                    

TABLE 4 summarizes the film properties and appearance characteristics of the cured coatings obtained by curing composition H.

This example illustrates that a sulfonimide cure catalyst of the invention produces excellent powder coating with Alftalat® AN 745 as well as Arakote® 3109 polyesters at two different temperatures.

                  TABLE 4                                                          ______________________________________                                         Powder Coatings with Alftalat ® AN 745 and                                 Powderlink ® 1174 Cured with a Sulfonimide Cure Catalyst                                   CURABLE                                                                        COMPOSITION H                                                                  175° C. Cure                                                                      190° C. Cure                                  ______________________________________                                         FILM APPEARANCE   Orange Peel Orange Peel                                                        Microblisters                                                                              Microblisters                                    FILM PROPERTIES                                                                Film Thickness    2.3-2.8     2.1-2.5                                          (mils)                                                                         Film Thickness    0.058-0.071 0.053-0.064                                      (mm)                                                                           Hardness, KHN.sub.25                                                                             10.9        10.5                                             MEK Rubs          200+        200+                                             Impact F/R (in-lb)                                                                               160/160     160/160                                          Color, Tristim-   -0.07       -0.06                                            ulus                                                                           Gloss, 60° 92.7        91.4                                             Gloss, 20° 77.1        73.4                                             RESISTANCE PROPERTIES                                                          Humidity (60° C.),                                                                        432         504                                              Time (hrs)                                                                     Appearance        Increased   No                                               (after testing)   Microblisters                                                                              Change                                           Salt Spray,       1070        1070                                             Time (hrs)                                                                     Creepage (mm)     1           1                                                Appearance        No Change   No Change                                        (after testing)                                                                ______________________________________                                    

EXAMPLE 6

Curable compositions 1 was prepared by the method described in EXAMPLE 2. It was cured at 175 and 190° C. by the method described in EXAMPLE 2.

    ______________________________________                                         COMPOSITION I            Weight (g)                                            ______________________________________                                         Rucote ® 101 polyester (solid)                                                                      94.00                                                 Powderlink ® 1174 Crosslinking                                                                      6.00                                                  Agent (solid)                                                                  Sulfonimide cure catalyst of EXAMPLE 1,                                                                 0.50                                                  PART A                                                                         Benzoin (a solid additive)                                                                              2.40                                                  R960-48 titanium dioxide pigment                                                                        40.00                                                 Resiflow III flow control agent                                                                         1.30                                                  ______________________________________                                    

TABLE 5 summarizes the film properties and appearance characteristics of the cured coatings obtained by curing composition H.

This example illustrates that a sulfonimide cure catalyst of Example 1, Part A produces excellent powder coatings with Rucote® 101 as well as Alftalat® AN 745 and Arekote® 3109 polyesters at two different temperatures.

                  TABLE 5                                                          ______________________________________                                         Powder Coatings with Rucote ® 101 and Powderlink ® 1174                Cured with a Sulfonimide Cure Catalyst                                                         CURABLE                                                                        COMPOSITION I                                                                  175° C. Cure                                                                      190° C. Cure                                  ______________________________________                                         FILM APPEARANCE   Orange Peel Orange Peel                                                        Microblisters                                                                              Microblisters                                    FILM PROPERTIES                                                                Film Thickness    2.0-2.6     1.7-2.4                                          (mils)                                                                         Film Thickness    0.051-0.066 0.043-0.061                                      (mm)                                                                           Hardness KHN.sub.25                                                                              11.9        10.8                                             MEK Rubs          200+        200+                                             Impact F/R (in-lb)                                                                               160/160     160/160                                          Color, Tristim-   -0.06       -0.07                                            ulus                                                                           Gloss, 60° 83.5        91.7                                             Gloss, 20° 66.7        74.6                                             RESISTANCE PROPERTIES                                                          Humidity (60° C.),                                                                        336         504                                              Time (hrs)                                                                     Appearance        Some loss   No Change                                        (after testing)   of gloss                                                     Salt Spray,       1070        1070                                             Time (hrs)                                                                     Creepage (mm)     1           3                                                Appearance        Some blisters                                                                              Some blisters                                    (after testing)                                                                ______________________________________                                    

EXAMPLE 7

An additional sulfonimide cure catalyst was prepared by the method of EXAMPLE 1, PART A, using the same reaction conditions but different reactants:

di-(4-Chlorobenzene)sulfonimide, prepared from 4-chlorobenzenesulfonamide and 4-chlorobenzenesulfonyl chloride.

Two additional curable compositions were prepared as follows:

    ______________________________________                                                             Weight (g)                                                 ______________________________________                                         COMPOSITION J                                                                  Arakote ® 3109 polyester (solid)                                                                 94.00                                                    Powderlink ® 1174 Crosslinking                                                                   6.00                                                     Agent (solid)                                                                  di-(Benzene)sulfonimide cure catalyst                                                                0.30                                                     Benzoin (a solid additive)                                                                           1.40                                                     R960-48 titanium dioxide pigment                                                                     40.00                                                    Resiflow P67 flow control agent                                                                      1.30                                                     COMPOSITION K                                                                  Arakote ® 3109 polyester (solid)                                                                 94.00                                                    Powderlink ® 1174 Crosslinking                                                                   6.00                                                     Agent (solid)                                                                  di-(4-Chlorobenzene)sulfonimide                                                                      0.30                                                     cure catalyst                                                                  Benzoin (a solid additive)                                                                           1.40                                                     R960-48 titanium dioxide pigment                                                                     40.00                                                    Resiflow P-67 flow control agent                                                                     1.25                                                     ______________________________________                                    

Compositions J and K, along with Composition E from EXAMPLE 4 were cured at 190° C./20 min by the method of EXAMPLE 2. The results are summarized in TABLE 6.

This example illustrates that both symmetrical and unsymmetrical sulfonimide cure catalyst of the invention are effective catalysts. It further illustrates that N-(methanesulfonyl)-p-toluenesulfonamide sulfonimide cure catalyst produces excellent film properties and acceptable appearance.

                  TABLE 6                                                          ______________________________________                                         Effect of Symmetrical and Unsymmetrical                                        Cure Catalyst on Film Properties and Appearance                                           CURABLE COMPOSITIONS                                                           Comp.   Comp.     Comp.                                                        E       J         K                                                 ______________________________________                                         FILM         Orange    Orange    Orange                                        APPEARANCE   Peel      Peel      Peel                                                       Micro-    Micro-    Micro-                                                     blisters  blisters  blisters                                                             Some      Wrinkles                                                             Wrinkles                                                FILM PROPERTIES                                                                Film Thickness                                                                              2.4-2.9   2.0-3.0   1.8-2.2                                       (mils)                                                                         Film Thickness                                                                              0.061-0.074                                                                              0.051-0.076                                                                              0.046-0.056                                   (mm)                                                                           Hardness, KHN.sub.25                                                                        12.1      12.4      11.8                                          MEK Rubs        20/200+                                                                               200+      200+                                          Impact F/R (in-lb)                                                                          160/160   160/160   110-120/40-50                                 Color, Tristim-                                                                             -0.06     -0.04     0.05                                          ulus                                                                           Gloss, 60°                                                                           92.7      93.9      95.1                                          Gloss, 20°                                                                           78.6      75.0      81.8                                          RESISTANCE                                                                     PROPERTIES                                                                     Humidity (60° C.),                                                                   456       600       600                                           Time (hrs)                                                                     Appearance   Loss of   No change No change                                     after testing                                                                               gloss                                                             Salt Spray,  1008      1008      1008                                          Time (hrs)                                                                     Creepage (mm)                                                                               1         0         0                                             Appearance   9         9         9                                             after testing                                                                  ______________________________________                                    

EXAMPLE 8

This example illustrates that a large variety of non-sulfonimide compounds are unsuitable as catalysts in the composition of this invention, when compared to Composition E of Example 4 under the same conditions. The results are summarized in Table 7.

It is concluded from the results in Table 7 that Composition E containing the sulfonimide of Example 1, Part A, has better overall properties when compared with related catalyst systems.

                                      TABLE 7                                      __________________________________________________________________________     COMPARISON OF FILM PROPERTIES OF SULFONIMIDES                                  WITH OTHER CATALYSTS IN POWDER COATINGS                                                                      GLOSS                                                                               APPEARANCE                                                 MEK RUBS                                                                              IMPACT, F/R                                                                            60°/20°                                                               BEFORE TESTING                              __________________________________________________________________________     Composition E Containing                                                                      20/200+                                                                               160/160 92.7/78.6                                                                           Orange Peel                                 the Sulfonimide of                 Microblisters                               EXAMPLE 1, PART A                                                               ##STR20##     1/3    --      --   --                                           ##STR21##     1/5    --      --   --                                           ##STR22##     <1     --      --   --                                          NH.sub.2 SO.sub.3 H                                                                           1/12   --      --   --                                           ##STR23##     200+   160/120-140                                                                            71.8/23                                                                             Wrinkles Craters                             ##STR24##     200+   60-80/0-20 (Fail)                                                                      79.4/32.8                                                                           Orange Peel Microblisters Pinholes           ##STR25##     50/200 50-60/0-5                                                                              29.4/6.4                                                                            Textured                                    __________________________________________________________________________

EXAMPLE 9

This example illustrates that powder coating compositions of the invention containing sulfonimide cure catalyst of the invention cure faster and produce films with superior overall film properties and appearance characteristics than similar compositions containing benzoin tosylate as the cure catalyst.

The following curable compositions, Curable Composition L and Curable composition M, were formulated and thereafer cured at 175° C. (20 min) and at 190° C. (20 min.) the procedure of EXAMPLE 2.

    ______________________________________                                                            Weight (g)                                                  ______________________________________                                         COMPOSITION L                                                                  Arakote ® 3109 polyester (solid)                                                                94.00                                                     Powderlink ® 1174 Crosslinking                                                                  6.00                                                      Agent (solid)                                                                  Sulfonimide Cure catalyst of                                                                        0.5                                                       EXAMPLE 1, PART A                                                              Benzoin (a solid additive)                                                                          2.4                                                       R960-48 titanium dioxide pigment                                                                    40.00                                                     Resiflow P-67 flow control agent                                                                    1.3                                                       COMPOSITION M                                                                  Arakote ® 3109 polyester (solid)                                                                94.00                                                     Powderlink ® 1174 Crosslinking                                                                  6.0                                                       Agent (solid)                                                                  Benzoin tosylate (solid)                                                                            2.0                                                       Benzoin (a solid additive)                                                                          1.4                                                       R960-48 titanium dioxide pigment                                                                    40.00                                                     Resiflow P-67 flow control agent                                                                    1.25                                                      ______________________________________                                    

Table 8 summarizes the film properties and appearance characteristics of the cured films obtained by curing the comparative pair (Compositions L and M) at 175° C. Table 9 depicts the same at 190° C.

It is concluded from the results in Tables 8 and 9 that films obtained by curing the compositions of the invention have superior film properties and appearance characteristics than similar films cured with benzoin tosylate. It can also be concluded that higher levels of benzene tosylate catalyst are needed to achieve cure compared to sulfonimide catalysts.

                  TABLE 8                                                          ______________________________________                                         Comparison of a Sulfonimide Cure Catalyst                                      of the Invention with                                                          Benzoin Tosylate in Powder Coatings Cured at 175° C.                                              Benzoin                                                              Sulfonimide*                                                                             Tosylate                                                             Curable   Curable                                                              Comp. L   Comp. M                                              ______________________________________                                         FILM APPEARANCE   Orange Peel Orange Peel                                                        Microblisters                                                                              Microblisters                                    FILM PROPERTIES                                                                Film Thickness    1.5-2.2     2.0-2.2                                          (mils)                                                                         Film Thickness    0.038-0.056 0.051-0.059                                      (mm)                                                                           Hardness, KHN.sub.25                                                                             11.3        11.9                                             MEK Rubs             20/200+   1/15                                            Impact F/R (in-lb)                                                                               160/160     20-30/0-5                                        Color, Tristim-   -0.06       -0.06                                            ulus                                                                           Gloss, 60° 81.1        92.4                                             Gloss, 80° 56.5        79.5                                             RESISTANCE PROPERTIES                                                          Humidity (60° C.),                                                                        504         96                                               Time (hrs)                                                                     Appearance        No change   Loss of Gloss                                    after testing                                                                  Salt Spray,       888         528                                              Time (hrs)                                                                     Creepage (mm)     3           0                                                Appearance        Blisters    Blisters                                         after testing                                                                  ______________________________________                                          *N-Methanesulfonyl-p-Toluenesulfonamide, sulfonimide catalyst of EXAMPLE       1, PART A                                                                

                  TABLE 9                                                          ______________________________________                                         Comparison of a Sulfonimide Cure Catalyst                                      of the Invention with Benzoin Tosylate in Powder                               Coatings Cured at 190° C.                                                                      Benzoin                                                              Sulfonimide*                                                                             Tosylate                                                             Curable   Curable                                                              Composition L                                                                            Composition M                                           ______________________________________                                         FILM APPEARANCE                                                                               Orange Peel Orange Peel                                                        Microblisters                                                                              Microblisters                                       FILM PROPERTIES                                                                Film Thickness 1.5-2.2     1.6-2.0                                             (mils)                                                                         Film Thickness 0.038-0.056 0.041-0.056                                         (mm)                                                                           Hardness, KHN.sub.25                                                                          11.2        11.6                                                MEK Rubs       200+        200+                                                Impact F/R (in-lb)                                                                            160/160     150-160/150-160                                     Color, Tristim-                                                                               -0.05       -0.06                                               ulus                                                                           Gloss, 60°                                                                             93.5        94.4                                                Gloss, 80°                                                                             74.9        83.4                                                RESISTANCE                                                                     PROPERTIES                                                                     Humidity (60° C.),                                                                     504         264                                                 Time (hrs)                                                                     Appearance     No change   Increased                                           after testing              Microblisters                                       Salt Spray,    960         528                                                 Time (hrs)                                                                     Creepage (mm)  4           0                                                   Appearance     Blisters    Blisters                                            after testing                                                                  ______________________________________                                          *N-Methanesulfonyl-p-Toluenesulfonamide, sulfonimide catalyst of EXAMPLE       1, PART A                                                                

EXAMPLE 10

This example illustrates that solvent-based coating compositions of the invention containing a sulfonimide cure catalyst cure at a rate comparable with sulfonic acid-cured compositions.

    ______________________________________                                                             Weight (g)                                                 ______________________________________                                         COMPOSITION N                                                                  JONCRYL ® 500 Acrylic                                                                            81.25                                                    Resin (80% Solids)                                                             CYMEL ® 1168 Crosslinking Agent                                                                  35.00                                                    di-Benzenesulfonimide (52% Solution)                                                                 1.00                                                     n-Butanol             20.00                                                    Xylene                16.55                                                    Non-Volatiles: 65 weight %                                                     Resin/Crosslinker                                                              Weight Ratio: 65/35                                                            Catalyst based on                                                              resin solid: 0.5 Weight %                                                      COMPOSITION O                                                                  JONCRYL ® 500 Acrylic                                                                            81.25                                                    Resin (80% Solids)                                                             CYMEL ® 1168 Crosslinking Agent                                                                  35.00                                                    p-Toluenesulfonic Acid (40 Wt %                                                                      0.75                                                     Solution)                                                                      n-Butanol             20.00                                                    Xylene                16.55                                                    Non-Volatiles: 65 Weight %                                                     Resin/Crosslinker                                                              Weight Ratio: 65/35                                                            Catalyst based on                                                              resin solids: 0.3 Weight %                                                     ______________________________________                                    

Curing of Compositions N and O

The curable compositions N and O were applied on Bonderite 100 Cold Roll Steel (CRS) substrate panels by means of a #46 wire cator applicator and were cured by heating at a cure schedule of 30 minutes at 121° C. (250° F.). The cured film was evaluated by standard methods widely accepted by the coatings industry. The physical properties of the cured films obtained by curing Composition N and Composition O are listed in Table 10. Table 10 shows that the composition cure rates are comparable. This is unexpected since the acidity of sulfonimide catalysts is lower than p-toluenesulfonic acid for comparable cures. The potlife is also improved and the appearance of the cured film is better.

It is concluded from this example that sulfonimide cure catalysts of this invention are effective catalysts in solvent-based coatings, and that they cure at a rate comparable to the widely used sulfonic acid catalysts.

                  TABLE 10                                                         ______________________________________                                         Cure Response of Solvent-Based Coatings                                        Comparison of Sulfonimide and Sulfonic Acid Catalysts                                     COMPOSITION COMPOSITION                                                        N.sup.(a)   O.sup.(b)                                               ______________________________________                                         Film Thickness                                                                 Mils         1.65-1.75     1.65-1.75                                           mm           0.042-0.044   0.042-0.044                                         121° C./30 min Cure                                                     Hardness, KHN.sub.25                                                                        8.0           9.0                                                 MEK Rubs     200+          200+                                                135° C./30 min Cure                                                     Hardness, KHN.sub.25                                                                        9.7           9.6                                                 MEK Rubs     .sup.  200+.sup.(c)                                                                          200+                                                149° C./30 min Cure                                                     Hardness, KHN.sub.25                                                                        10.1          10.0                                                MEK Rubs     200+          200+                                                ______________________________________                                          .sup.(a) Composition containing dibenzonesulfonimide.                          .sup.(b) Composition containing p-toluenesulfonic acid.                        .sup.(c) Film scratches off with difficulty using fingernail immediately       after 200 double rubs (film scratched while wet with MEK).               

EXAMPLE 11

This example illustrates lower yellowing of sulfonimide-cured compositions relative to sulfonic acid cured compositions in base coat/clear coat solvent-based coatings under overbake cure conditions.

White Base Coat

The base coat was prepared by a procedure similar to the procedure described in Example 10 using the following ingredients and conditions:

    ______________________________________                                                               Weight (g)                                               ______________________________________                                         Base Coat Formulation A                                                        JONCRYL ® 500 Acrylic                                                                              60.00                                                  Resin Solids (80% Solids)                                                      OR-650 Titanium Dioxide Pigment                                                                        80.00                                                  Methyl Amyl Ketone      18.00                                                  BYK ® P 104-S Wetting Agent                                                                        0.80                                                   (a product of Byk-Mallinckrodt Company,                                        Wallingford, CT)                                                               Base Coat Formulation B                                                        JONCRYL ® 500 Acrylic                                                                              40.00                                                  Resin Solids (80% Solids)                                                      CYMEL ® 303 Crosslinking Agent                                                                     20.00                                                  n-Butanol               15.00                                                  p-Toluenesulfonic Acid (40% Solution)                                                                  1.00                                                   ______________________________________                                    

After grinding Formulation A in a 3-roll mill, Formulation B was added to ground Formulation A, and applied to ED-3150A primed EP1-P60 panel, available from Advanced Coating Technologies, Hillsdale, Mo., using a #34 wire cator applicator. The resulting panels were cured at 121° C. (250° F.) for 15 minutes, and thereafter the clear topcoat Composition P and Composition Q (infra) were each applied to two separate panels coated with the base coat.

Clear Top Coat Compositions

    ______________________________________                                                               Weight (g)                                               ______________________________________                                         COMPOSITION P                                                                  JONCRYL ® 500 Acrylic                                                                              81.30                                                  Resin (80% Solids)                                                             CYMEL ® 1170 Crosslinking Agent                                                                    35.00                                                  di-Benzenesulfonimide   0.52                                                   n-Butanol               16.00                                                  Xylene                  21.50                                                  Non-Volatiles: 65 Wt. %                                                        Resin/Crosslinker Weight Ratio: 65/35                                          Catalyst based on Resin Solids: 0.5 Wt. %                                      COMPOSITION Q                                                                  JONCRYL ® 500 Acrylic                                                                              81.30                                                  Resin (80% Solids)                                                             CYMEL ® 1170 Crosslinking Agent                                                                    35.00                                                  p-Toluenesulfonic Acid  0.30                                                   n-Butanol               16.00                                                  Xylene                  21.50                                                  Non-Volatiles: 65 Wt. %                                                        Resin/Crosslinker Weight Ratio: 65/35                                          Catalyst based on Resin Solids: 0.3 Wt. %                                      ______________________________________                                    

The clear coat Compositions P and Q were each applied onto base-coated panels using a #46 wire cator applicator and thereafter cured; first at 121° C./30 minute cure followed by an additional 149° C./30 minute cure, simulating overbake condition which commonly occur in a coating process. The results are summaried in Table 11.

It is concluded from the results in Table 11 that the solvent-based coatings compositions of the invention containing the novel sulfonimide cure catalysts of the invention have better overbake tolerance than sulfonic acid catalyzed compositions when cured under overbake conditions.

                  TABLE 11                                                         ______________________________________                                         Yellowing of Solvent-Based Base-Coat/Clear-Coat                                Coatings Under Overbake Conditions                                             Comparison of Sulfonimide and Sulfonic Acid Catalysts                                       COMPOSITION                                                                               COMPOSITION                                                         P.sup.(a)  Q.sup.(b)                                              ______________________________________                                         Film Thickness                                                                 mils/mm                                                                        Base Coat      1.26/0.032   1.28/0.032                                         Clear Coat     1.59/0.040   1.48/0.038                                         Hardness, KHN.sub.25                                                           (Clear Coat)                                                                   121° C./30 min cure                                                                    0.8          8.0                                                121° C./30 min cure +                                                                  9.3          10.3                                               149° C./30 min overbake                                                 Yellow Index                                                                   121° C./30 min cure                                                                    -1.56        -1.28                                              121° C./30 min cure +                                                                  +2.18        +5.32                                              149° C./30 min overbake                                                 Total Color Change                                                                            2.71         4.39                                               (difference of E)                                                              ______________________________________                                          .sup.(a) Composition containing dibenzonesulfonimide.                          .sup.(b) Composition containing ptoluenesulfonic acid.                   

EXAMPLE 12

This example illustrates an embodiment in which a 1:1 blend of sulfonimide cure catalyst and polyfunctional material is used to obtain Composition R, which is a curable composition containing catalyst/polyfunctional material combination of the invention.

PREPARATION OF CATALYST/POLYFUNCTIONAL MATERIAL COMBINATION

A mixture of dibenzenesulfonimide (10.0 g) and Alftalat® AN745 solid polyester (10.0 g) was melt-mixed at 150° C. The resinous material thus obtained was cooled to room temperature and the resulting solids crushed to give a catalyst/polyfunctional material combination usable in the method of the invention.

    ______________________________________                                         COMPOSITION R           Weight (g)                                             ______________________________________                                         Arakote ® 3109 polyester (solid)                                                                   93.50                                                  Powderlink ® 1174 crosslinking agent (solid)                                                       6.00                                                   Catalyst/polyfunctional material combination                                                           1.00                                                   of this example as prepared above                                              containing 1:1 weight ratio of dibenzene-                                      sulfonimide and Alftalat ® AN745 polyester                                 Benzoin (a solid additive)                                                                             1.40                                                   R960-48 Titanium dioxide pigment                                                                       40.00                                                  Resiflow P67 flow control agent                                                                        1.30                                                   ______________________________________                                    

Composition R was cured at 190° C./20 min by the method of EXAMPLE 2. The results are summarized in TABLE 12. As seen from Table 12, good film appearance (no wrinkles), film properties such as cure, impact, and gloss, and resistance properties such as resistance to humidity and salt spray are obtained. This embodiment, therefore, is within the scope of the invention.

                  TABLE 12                                                         ______________________________________                                         Powder Coatings Prepared by Using a                                            Catalyst/Polyfunctional Material Combination.sup.a                             in a Curable Composition (Composition R)                                       ______________________________________                                         FILM APPEARANCE   Orange Peel, Microblisters,                                                    Microcraters in some areas,                                                    No Wrinkles                                                  FILM PROPERTIES                                                                Film Thickness                                                                 (mils)            1.3-2.4                                                      (mm)              0.033-0.061                                                  Hardness, KHN.sub.25                                                                             11.2                                                         MEK Rubs          200+                                                         Impact F/R (in-lb)                                                                               160/160                                                      Color, Tristimulus                                                                               -0.08                                                        Gloss,                                                                         60°        95.3                                                         20°        83.3                                                         RESISTANCE PROPERTIES                                                          Humidity (60° C.), Time (hrs)                                                             504                                                          Appearance After Testing                                                                         No Change                                                    Salt spray, Time (hrs)                                                                           1008                                                         Creepage (mm)     0                                                            Appearance After Testing                                                                         No Change                                                    ______________________________________                                          a. Dibenzenesulfonimide/Alftalat ® AN745 Polyester (1:1 weight ratio)      combination at 1 wt % level based on total resin solids, corresponding to      0.5 wt % level of dibenzonesulfonimide based on total resin solids in          Composition R.                                                           

EXAMPLE 13

The experiment of Example 12 was repeated with the following modifications:

1. Masterbatching was carried out using phenyl-p-tolylsulfonimide instead of dibenzenesulfonimide.

2. COMPOSITION S was prepared by using the masterbatch described in Example 13, part 1 (above) instead of the dibenzenesulfonimide masterbatch in Composition R of Example 12.

3. COMPOSITION T was prepared by replacing the Arakote® 3109 polyester in Composition S with Alftalat® AN745 polyester.

4. COMPOSITION U was prepared by replacing the Arakote® 3109 polyester in Composition S with Rucote® 101 polyester.

Table 13 summarizes the results obtained by curing the compositions S, T, and U by the 190° C./20 min protocol described in Example 12. The embodiments represented by Compositions S, T, and U, having good film properties, are also within the scope of the invention.

                                      TABLE 13                                     __________________________________________________________________________     EXAMPLE 13                                                                     Powder Coatings Prepared by Using Phenyl-p-tolylsuflonimide/                   Alftalat AN745 Polyester Combination                                                           COMPOSITION                                                                               COMPOSITION                                                                             COMPOSITION                                                S          T        U                                          __________________________________________________________________________     FILM APPEARANCE Orange Peel                                                                               Orange Peel                                                                             Orange Peel                                                Microblisters                                                                             Microblisters                                                                           Microblisters                                              Microcraters on edges                                          FILM PROPERTIES                                                                Film Thickness                                                                 (mils)          1.5-3.1    1.7-2.4  1.6-2.4                                    (mm)            0.038-0.079                                                                               0.043-0.061                                                                             0.041-0.061                                Hardness, KHN.sub.25                                                                           11.8       11.3     11.1                                       MEK Rubs        200+       200+     200+                                       Impact F/R (in-lb)                                                                             160/160    160/160  160/160                                    Color, Tristimulus                                                                             -0.09      -0.09    -0.09                                      Gloss,                                                                         60°      93.2       94.0     91.1                                       20°      72.3       72.3     75.4                                       RESISTANCE PROPERTIES                                                          Humidity (60° C.), Time (hrs)                                                           504        504      504                                        Appearance After Testing                                                                       No Change  No Change                                                                               No Change                                  Salt Spray, Time (hrs)                                                                         1056       1056     528                                        Creepage (mm)   0          0        0                                          Appearance After Testing                                                                       No Change  few blisters                                                                            blisters                                   __________________________________________________________________________

Although the present invention has been described with reference to certain preferred embodiments, it is apparent that modifications and changes thereof may be made by those skilled in the art, without departing from the scope of this invention as defined by the appended claims. 

What is claimed is:
 1. A curable composition comprising:(i) a sulfonimide cure catalyst, (ii) an aminoplast crosslinking agent containing at least two crosslinkable groups, and (iii) a polyfunctional material capable of reacting with the aminoplast crosslinking agents,wherein the weight ratio of crosslinker to polyfunctional material (ii:iii) is from about 1:40 to about 3:1, and wherein the sulfonimide cure catalyst is selected from the group consisting of: (a) a sulfonimide represented by the formula

    RSO.sub.2 NZSO.sub.2 R

wherein each of the R groups is, independently, selected from the group consisting of (a1) a linear, branched or cyclic alkyl, fluoroalkyl or N,N-dialkylamino group of 1 to 20 carbon atoms, or mixtures thereof, (a2) an aryl group of 1 to 20 carbon atoms containing 5 or less aromatic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴ and R⁵ groups, wherein R¹, R², R³, R⁴ and R⁵ groups are the same or different groups selected from the group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto, vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkyl aminocarbonyl and N,N-dialkyl aminocarbonyl groups, and (a3) an aralkyl group wherein the alkyl and the aryl groups have the same meaning as the alkyl and aryl groups (a1) and (a2), andwherein the Z group is (a4) hydrogen, (a5) acyl or (a6) an alkyl or aralkyl group of 1 to 20 carbon atoms; (b) a sulfonimide represented by the formula

    --(R'--SO.sub.2 NH--SO.sub.2)--.sub.n

wherein n groups of the --(R'--SO₂ NH--SO₂)-- units may be the same or different, and the R' group in each of the n units is independently selected from the group consisting of (b1) a linear, branched or cyclic alkylene or fluoroalkylene group of 1 to 20 carbon atoms, (b2) an arylene group of 1 to 20 carbon atoms containing 5 or less carbocyclic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴ and R⁵ groups, wherein R¹, R², R³, R⁴ and R⁵ groups are the same or different groups selected from the group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto, vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkyl aminocarbonyl and N,N-dialkyl aminocarbonyl groups, and (b3) an aralkylene group wherein the alkylene and the arylene groups have the same meaning as the alkylene and arylene groups (b1) and (b2); (c) a sulfonimide represented by the formula

    P--(SO.sub.2 NHSO.sub.2 R").sub.n

wherein P is a polyfunctional group or a polymer of a number average molecular weight greater than 500, R" is an alkyl or aryl group of 1 to 20 carbon atoms, and n is 2 or greater; and (d) a latent reactive form thereof.
 2. The composition of claim 1 wherein the reactive group of the polyfunctional aminoplast reactive material (iii) is selected from a group consisting of carboxy, hydroxy, carbamate, amino, amido, mercapto group and mixtures thereof.
 3. The composition of claim 2 wherein the polyfunctional material (iii) has a number average molecular weight between from about 100 to about 50,000.
 4. The composition of claim 2 wherein the polyfunctional material (iii) is a solid at 40° C.
 5. The composition of claim 2 wherein the polyfunctional material is a hydroxy functional acrylic resin or a hydroxy functional polyester resin.
 6. The composition of claim 2 wherein the polyfunctional material is a carboxy functional acrylic resin or a carboxy functional polyester resin.
 7. The composition of claim 1 wherein the weight ratio of the sulfonimide catalyst (i) to the aminoplast crosslinking agent (ii) is from about 1:4 to about 1:400.
 8. The composition of claim 1 wherein the sulfonimide cure catalyst is from about 0.01 to about 10 weight percent of the total weight of the resin forming ingredients in the composition.
 9. The composition of claim 1 wherein the aminoplast resin (ii) is represented by the formula:

    A--(R).sub.n

wherein n is the number of R groups and is at least 2, A is a substituted polyamino anchor molecule connected to n(R) groups via the amino nitrogen, and each R is independently selected from the group consisting of hydroxymethyl, alkoxymethyl, an aminoplast containing oligomeric group, hydrogen, alkyl of 1 to 10 carbon atoms, and mixtures thereof; with the proviso that at least two R groups are selected from the group consisting of hydroxymethyl, alkoxymethyl, an aminoplast containing oligomeric group, and mixtures thereof.
 10. The composition of claim 9 wherein the polyamino anchor molecule of A--(R)_(n) is derived from monomeric or oligomeric polyamino molecules selected from the group consisting of glycoluril, melamine, benzoguanamine, cyclohexanecarboguanamine, acetoguanamine, urea, substituted linear and cyclic ureas, polycarbamates, polyhydantoins, polyamides and mixtures thereof.
 11. The composition of claim 9 wherein the aminoplast crosslinking agent (ii) is an N-substituted glycoluril represented by the formula: ##STR26## wherein at least two of the R groups are selected from the group consisting of hydroxymethyl, methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, pentoxymethyl, hexoxymethyl, heptoxymethyl, octoxymethyl, nonoxymethyl, decoxymethyl, and mixtures thereof, and the remaining R groups are hydrogen, alkyl, or glycoluril group-containing oligomeric moieties.
 12. The composition of claim 11 wherein the number of the methoxymethyl groups is from about 2.5 to about 4.0.
 13. The composition of claim 12 wherein the equivalent weight of the glycoluril is from about 79.5 to about 127.2.
 14. The composition of claim 11 wherein the glycoluril crosslinking agent is represented by the formula: ##STR27##
 15. The composition of claim 1 wherein the sulfonimide cure catalyst is represented by the formula: ##STR28## wherein X is independently selected from the group consisting of hydrogen, chloro, methyl, alkyl, nitro, amino, cyano, alkoxycarbonyl, carboxyl, acyl, M-alkylamino-carbonyl, and N,N-dialkylaminocarbonyl groups.
 16. Composition of claim 15 wherein the sulfonimide cure catalyst is represented by the formula: ##STR29##
 17. Composition of claim 15 wherein the sulfonimide cure catalyst is represented by the formula: ##STR30##
 18. Composition of claim 15 wherein the sulfonimide cure catalyst is represented by the formula: ##STR31##
 19. Composition of claim 1 wherein the sulfonimide cure catalyst is represented by the formula: ##STR32##
 20. The composition of claim 1 contained in a liquid medium.
 21. The composition of claim 20 wherein the medium is a solvent for ingredients (i), (ii), and (iii).
 22. The composition of claim 21 wherein the solvent is selected from water, alcohols, ketones, ethers, esters, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and mixtures thereof.
 23. The composition of claim 20 wherein the sulfonimide cure catalyst of ingredient (i) is represented by the formula: ##STR33## wherein X is independently selected from the group consisting of hydrogen, chloro, methyl, alkyl, nitro, amino, cyano, alkoxycarbonyl, carboxyl, acyl, N-alkylamino-carbonyl, and N,N-dialkylaminocarbonyl groups.
 24. The composition of claim 23 wherein the sulfonimide cure catalyst is represented by the formula: ##STR34##
 25. The composition of claim 23 wherein the sulfonimide cure catalyst is represented by the formula: ##STR35##
 26. The composition of claim 23 wherein the sulfonimide cure catalyst is represented by the formula: ##STR36##
 27. The composition of claim 20 wherein the sulfonimide cure catalyst is represented by the formula: ##STR37##
 28. The composition of claim 1 wherein at least one of ingredients (i), (ii), and (iii) is a solid at 40° C.
 29. The composition of claim 28 wherein all of ingredients (i), (ii), and (iii) are solids.
 30. The composition of claim 28 in the form of a flowable powder.
 31. A solid object formed by thermally curing the composition of claim
 1. 32. The composition of claim 1 comprising:(i) a sulfonimide cure catalyst represented by the formula

    RSO.sub.2 NZSO.sub.2 R

wherein each of the R groups is, independently, selected from the group consisting of (a1) a linear, branched or cyclic alkyl, fluoroalkyl or N,N-dialkylamino group of 1 to 20 carbon atoms, or mixtures thereof, (a2) an aryl group of 1 to 20 carbon atoms containing 5 or less aromatic or heterocyclic aromatic rings substituted by R¹, R², R³, R⁴ and R⁵ groups, wherein R¹, R², R³, R⁴ and R⁵ groups are the same or different groups selected from the group consisting of hydrogen, fluoro, alkyl, fluoroalkyl, aryl, haloaryl, carboxy, mercapto, vinyl, chloro, bromo, cyano, nitro, sulfonyl, acyl, alkoxycarbonyl, alkoxy, perfluoroalkoxy, hydroxy, amino, acylamino, alkoxycarbonylamino, carbamoyl, aminocarbonyl, N-alkyl aminocarbonyl and N, N-dialkyl aminocarbonyl groups, and (a3) an aralkyl group wherein the alkyl and the aryl groups have the same meaning as the alkyl and aryl groups (a1) and (a2), andwherein the Z group is (a4) hydrogen, (a5) acyl or (a6) an alkyl or aralkyl group of 1 to 20 carbon atoms; (ii) a glycoluril crosslinking agent represented by the formula ##STR38## and (iii) a hydroxy functional polyester resin. 